Thanks for the advice Sam. Following your recommendations I downgraded:

Crypt-DH 0.06 to Crypt-DH 0.03
Crypt-DSA 0.14 to Crypt-DSA 0.12

and it's now working much better. I don't fully understand the link between the Crypt and PERI modules but can leave that bit of it for now.

I now need to rewrite the "fatal_disconnect" code so that the system doesn't terminate the whole program if it can't connect, but that's a whole different set of problems!